In a variety of subsea applications, the production of oil, hydrocarbons, or other production fluids from subsea production zones may be limited, restricted, or written off entirely due to the presence of water within the production zone. Specifically, as the production fluids are produced from a zone, and as the zone depletes, water may permeate into the pipeline, decreasing the production, lowering the pressure or the production zone, and generally hindering profitability of a well system. In some instances, this decrease in productivity, caused by the influx of water, necessitates the temporary shutdown of a well system, or a complete abandonment of a reserve as unprofitable. Additionally, fluids from the subsea production zones may be directed from one locale to another. Depending on the activity, fluid may be directed through subsea flowlines located on the seafloor or directed upwardly from a subsea well, pipe or pipeline, pipeline end termination (PLET), a vessel, or other container to the water surface. In some cases a subsea pump is used to direct subsea fluids from one locale to another.
In one known subsea pumping technique, hydraulic drive systems have been employed for powering subsea pumps. However, the motor powering the pump may have to overcome a given hydrostatic pressure when returning motor fluids back to the water surface, and the result may include a time intensive endeavor placing an unwanted load on the motor powering the subsea pump.
In another known subsea pumping technique, electric drive systems have been employed to power subsea pumps. However, at great depths it may be difficult to supply the necessary current and amperage to effectively pump fluids to the water surface.
A more efficient technique for transporting subsea fluid and maintaining productivity in subsea production zones is desired.
In petroleum production, oil and its byproducts are typically removed from wells and transported through pipelines, including subsea pipelines. The flow of oil and other fluids through a subsea pipeline can lead to the buildup of different substances within the pipe impeding fluid flow there through. For example, scale, paraffin wax, wax plugs, paraffin plugs, hydrates, ice plugs, asphaltenes, debris or sand may build up in the pipeline over time depending on the nature of the fluid flowing through the pipeline and other surrounding circumstances.
One method to prevent the formation of paraffin deposits is to heat the pipelines. However, this method is very expensive and is not feasible for subsea pipelines submerged in the cold sea water.
Another method involves “pigging”, wherein a mechanical device is passed through the pipeline scraping the inner wall of the pipeline and pushing paraffin deposits through. However, the pigging tools (e.g., mechanical tools used for maintenance) then require removal, from the pipeline or well, for increasing or restoring the flow of hydrocarbons from subsea environments.
Another method for removing paraffin deposits is “hot oiling,” wherein a heated oil is pumped through the pipeline in order to remove the paraffin wax deposits. However, again this can be expensive and not very feasible for subsea environments.
Another cause of blockage in subsea pipelines is the formation of gas hydrates where an aqueous phase is inherently present, during the transportation of fluids including gases. This is a common problem, especially in deep sea conditions including low temperatures and/or high pressures. Low temperatures and the presence of water can lead to the formation of these gas hydrates in the pipelines.
One method of dealing with gas hydrates is to insulate the pipeline. But, this approach is typically expensive. Another method is to pump methanol through the pipeline or to use chemical methods, such as addition of anti-agglomerates (e.g. kinetic inhibitors or thermodynamic inhibitors). However, to be effective, large quantities of these chemicals are required making the process expensive.
Other problems associated with production of hydrocarbons can include increased hydrostatic pressure due to the accumulation of water in the pipeline or producing zone (e.g., a pipeline, a PLET, a producing well, or combinations thereof). Accordingly, improved systems and methods are needed for providing the flow, or increasing the flow, of hydrocarbons form a subsea environment to a surface and/or production facility.